Electrodeposition of copper from an acid bath



United States Patent ELECTRODEPOSITION OF COPPER FROM AN ACID BATH Edwin W. Hoover, Huntington Woods, Mich., assignor to The Udylite Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application May 26, 1952, Serial No. 290,092

10 Claims. (Cl. 204-52) This invention relates to the electrodeposition of copper from an aqueous acidic bath and more particularly concerns the utilization of selected addition agents to aqueous acidic baths for the purposes hereinafter stated.

The object of this invention is to decrease the grain size and increase the luster of the copper deposit without materially impairing the ductility of the plate or decreasing the current density range of the acidic copper plating bath.

It has been found that this object can be accomplished by the addition to acidic copper baths and especially to acidic copper sulfate baths of small concentrations of organic compounds having a structure characterized by the formula designated Formula A:

FORMULA A wherein R1, R2 and R3 are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals, and X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate. The anion X is relatively unimportant and in addition to the anions above given may be any one of a wide variety of other anions including organic anions such as formate, acetate, propionate, etc. It will be appreciated that the compounds represented by the above formula when present in an acid copper bath are highly ionized substances and the anion X is in ionic admixture with the other anions of the bath such as the sulfate anion, the nitrate anion, etc.

The class of compounds represented by Formula A which have been found to efiectively accomplish the above stated object are, in general, the diamino derivatives of the phenylphenazonium salts, which dyes are usually called the safranines. Illustrative examples of addition agents in the class of compounds having the above given formula which may be utilized in accordance with this invention and in the concentrations indicated, are shown in Table 1.

Table 1 Cone, gfi grams/liter grams/flier HzN -NH2 Phenosatranlne 2,707,167 Patented Apr. 26, 1955 Optimum Cone, grams/liter gfig iii H30 CH3 10 H2N NH, .002. 03 .003. 01

/N CI 5611 Tolusatranine (oHmN NH2 .002-.03 nos-.01

a C1 00H,

Fuchsia 4 (CZHQgN N(C2H5)2 .002-.03 mos-.01

I C(CuH Amethyst Violet 5, N

HN[l/ONHa 002-. 03 .003-. 01

Mauveine CH; -CH3 C2H5 NH2 N 002-. 03 003. 01

Cilia OK Diethyl Satranlne 0 OH: CH:

CH3 l g N 002-. 03 003-. 01 O a 0K Dlmethyl Safranine Mixtures of addition agents encompassed by Formula A and illustrated in Table 1 may also be used with beneficial efiects in concentrat1ons corresponding approximately to the concentrations indicated for the illustrative examples of Table 1, that is, the concentration of the mixture should fall within the range of concentration indicated for an individual example in Table 1. For v some purposes, especially in those instances in which the baths are used at temperatures substantially higher than room temperature, concentrations up to about .05 gram/ liter may be employed. For best bath life it is preferable to maintain a concentration of chloride, or its equivalent in bromide or iodide, of about .003 to about .020 gram/liter in the solution. It is to be understood that when X is either fluoride, sulfate, bisulfate or nitrate, that chloride, bromide or iodide ions in an amount equivalent to about .003 to .020 gram/liter of chloride is preferably present in addition. As initially made up, a solution containing a compound in which X is a halide other than fluoride, contains at least the preferred minimum halide concentration, but it is usually preferable to replenish the halide during use in order to maintain the minimum concentration of about .003 gram/liter of chloride or its equivalent.

Acidic copper baths having compositions varying over rather wide limits, may be employed. However, for the best grain refinement, rate of brightening and the widest bright plating range, the following basic bath composition designated Formula B is recommended for use:

FORMULA B C one Prceferred I grams/ht grar s l liter GuSO -5H2O H2804 The bath of Formula B is preferably operated at temperatures varying from room temperature to somewhat higher temperatures. For example, from about 17 C. to 40 C. (approximately 60 F. to 105 F.) may be used. Although it has been observed that warmer temperatures have a tendency to decrease the brightness of the plate which is produced, improved deposits may be obtained from baths operating at temperatures as high as about 50 C. It is desirable to have either cathode agitation or agitation of the bath, and uniform air agitation is preferred. Cathode current densities may vary between about 10-100 amps./ sq. ft. (approximately 1 to 10 amps/sq. dm.), with the variation within this range depending primarily upon the degree of the agitation of the cathode film and the shape of the article to be plated. For non-recessed, symmetrical shaped articles and high degrees of bath agitation, higher current densities approaching 100 amps./ sq. ft. are satisfactory, whereas for slow cathode film agitation and irregular shaped articles, it is advisable to use lower cathode current densities of about 20-40 amps/sq. ft. For general purposes, an average cathode current density of about 30 to 50 amps./ sq. ft. is satisfactory.

Nitric acid or phosphoric acid may be satisfactorily substituted for the sulfuric acid of Formula B in approximately equal proportions. Additionally, Formula B may include other ions for the purpose of increasing the conductivity of the solution such as sodium, potassium or ammonium ions. These ions may be introduced in the solution in the form of soluble salts such as sodium, potassium or ammonium nitrate, etc. Furthermore, the copper sulfate of Formula B may be satisfactorily replaced by copper nitrate in approximately equivalent quantities and when acidified with small amounts of phosphoric, nitric or sulfuric acids, the beneficial effect of reducing the grain size and increasing the luster of the deposit is also evident upon the addition of small concentrations of the addition agents of this invention. The copper nitrate baths are, however, somewhat inferior in the production of brightness of plate, to the copper sulfate baths. Satisfactory results are obtained from baths in which the concentration of copper sulfate or copper nitrate varies from as low as about 100 grams/liter up to saturation. Concentrations of acid above that which is equivalent in acidity to about 80 to 100 grams/liter of sulfuric acid tends to decrease the brightening effect caused by the presence in the solution of the addition agents of this invention, and such concentrations are therefore to be avoided.

Small concentrations of wetting agents may be present in the baths of this invention and their presence therein has been observed to reduce pitting and striation formation in the deposit due to the presence of harmful organic compounds or excessive concentrations of, brighteners. For example, the surface-active compounds, sodium decyl sulfate and the sulfated mono-ethylene oxide condtiusate of decyl alcohol when present in concentrations of about .01 to .06 grams/liter are especially effective. These wetting agents would normally cause excessive frothing upon air agitation, but in the presence of the addition agents of this invention, the frothing is minimized.

The following typical plating baths are given by Way of example to illustrate the invention in greater detail.

Example 1 CuSO4-5H2O 200 grams/liter. H2804 15 grams/liter. Diethyl safranine .002 gram/liter. Temperature 70 F.-95 F. Cathode current density 30-40 amps./ sq. ft. Air agitation.

Example 11 CuSO4-5H2O 200 grams/liter. H2804 15 grams/liter. Tolusafranine .008 gram/liter. Temperature 70 F.- F. Cathode current density 30-40 amps/sq. ft. Sodium decyl sulfate .03 gram/liter. Air agitation.

Example III CuSOr-SHzO 200 grams/liter. NH4NO3 20-30 grams/liter. H2504 a 15 grams/liter. Amethyst Violet .008 gram/liter. Temperature 70 F. F. Cathode current density 30-50 amps/sq. ft. Air agitation.

Example IV CU(NO3)2 200 grams/liter. HNOs 10 grams/liter. Mauveine .015 gram/liter. Temperature 70 F.-95 F. Cathode current density 40-60 amps./ sq. ft. Air agitation.

Example V CuSO4-5H2O 200 grams/liter. H2504 15 grams/liter. Fuchsia .02 gram/liter. Temperature 70 F.-95 F. Cathode current density 30-40 amps./ sq. ft. Air agitation.

Example VI CUSO4'5H2O 200 grams/liter. H2804 15 grams/liter. Phenosafranine .008 gram/liter. Temperature 70 F.-95 F. Cathode current density 30-40 amps/sq. ft. Air agitation.

What is claimed is:

1. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of copper salts and minor proportions of a compound having the structure:

wherein R1, R2 and R3 are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals and X is an anion selected from the group consistiug of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate.

2. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate and .002.03 grams/liter of a compound having the structure:

wherein R1, R2 and R3 are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals and X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate.

3. A bath for the electrodeposition of copper comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate and .002.03 grams/ liter of a material selected from the group consisting of Phenosafranine, Tolusafranine, Fuchsia, Amethyst Violet, Diethyl safranine, Dimethyl safranine and Mauveine.

4. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acid copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, said aqueous solution also containing minor proportions of a compound having the structure:

wherein R1, R2 and R3 are radicals selected from the group 5. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, said aqueous solution also containing minor proportions of a compound selected from a group consisting of Phenosafranine, Tolusafranine, Fuchsia, Amethyst Violet, Diethyl safranine, Dimethyl safranine and Mauveine.

6. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, said aqueous solution also containing about .002 to about .03 gram/liter of a compound having the structure:

wherein R1, R2 and Rs are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals and X is an anion selected from the group consulfate, bi-

wherein R1, R2 and R3 are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals and X is an anion selected from. the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate.

8. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003 gram/liter to about .020 gram/liter of chloride and a minor proportion of a compound having the structure:

wherein R1, R2 and R3 are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals and X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate. 1

9. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003 gram/liter to about .020 gram/liter of chloride, a minor proportion of a compound having the structure:

wherein R1, R2 and R3 are radicals selected from the group consisting of hydrogen, methyl, ethyl and phenyl radicals and X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and a small amount of a wetting agent.

10. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous: acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003

8 gram/ liter to about .020 gram/ liter of chloride, a minor wherein R1, R2 and R3 are radicals selected from the group proportion of a compound having the structure: consisting of hydrogen, methyl, ethyl and phenyl radicals N and X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and R, R: 5 nitrate, and a small amount of a wetting agent.

N N References Cited in the file of this patent 111 /N Rz UNITED STATES PATENTS X 10 2,291,590 Lind et a1. July 28, 1942 2,326,999 Lind et al. Aug. 17, 1943 2,602,774 Beaver July 8, 1952 

1. A BATH FOR THE ELECTRODEPOSITION OF COPPER, COMPRISING AN AQUEOUS ACIDIC SOLUTION OF COPPER SALTS AND MINOR PROPORTIONS OF A COMPOUND HAVING THE STRUCTURE: 